1. Field of the Invention
The present invention relates to a memory device and a method for driving the same. More particularly, the present invention relates to a memory device having a cell that has one transistor and one resistant element, in which the resistant element acts as a storing means, and a method for driving the memory device.
2. Description of the Related Art
In general, a memory device, particularly a unit memory cell in which data is written in a DRAM (dynamic random access memory), is constructed with one transistor and one capacitor. The capacitor represents a region in which data is written, namely, a data storage region. In order to prevent any data loss or data error when writing and reading data, the capacitor is required to have a certain electrostatic capacity.
As memory devices become more highly integrated, a region occupied by a capacitor in a memory cell becomes smaller. However, the electrostatic capacity of the capacitor required for storing data remains the same.
To increase the electrostatic capacity of a capacitor in a limited region, the region of the capacitor in which electrodes are positioned must be as large as possible, the distance between the electrodes as small as possible, and the dielectric material between the electrodes as conductive as possible.
By processing electrodes to have three-dimensional shapes such as cylindrical shapes, the region of the capacitor in which the electrodes are positioned may be enlarged. However, unlike manufacturing capacitors having two-dimensionally shaped electrodes, manufacturing a capacitor having such three-dimensionally shaped electrodes is difficult due to the structural complexity of the capacitor. By decreasing the thickness of the dielectric material, the distance between the electrodes may be decreased. However, a thin dielectric layer leads to increased leakage current. Using a dielectric material that is highly conductive greatly increases the electrostatic capacity of the capacitor compared to using a thin dielectric film. However, when manufacturing semiconductor devices using highly conductive materials as capacitor dielectrics, etching becomes more complicated and the product price increases because the materials used for the electrode are limited to precious metals having high etching resistance.
Due to the existing problems, the manufacturing process of a memory device using a capacitor as a storing means becomes more complex. As a result, manufacturing reproducibility and memory device reliability may be poor, leading to a sharp decrease in yield.